The present invention generally relates to carrier chrominance signal recording and/or reproducing apparatuses, and more particularly to a carrier chrominance signal recording and/or reproducing apparatus which shifts by a digital processing the phase of a chrominance subcarrier of a frequency converted carrier chrominance signal which is reproduced as crosstalk from adjacent tracks, when recording or reproducing a carrier chrominance signal within a color video signal on or from a recording medium according to the azimuth recording and reproducing system.
Among the helical scan type video tape recorders (VTRs) which employ the azimuth recording and reproducing system, the more popular VTRs record a frequency division multiplexed signal on video tracks on a magnetic tape by alternately forming the video tracks by a pair of rotary heads having gaps of mutually different azimuth angles at the time of a recording, and reproduce the frequency division multiplexed signal from the video tracks at the time of a reproduction. The frequency division multiplexed signal is made up of a frequency modulated luminance signal and a frequency converted carrier chrominance signal. The frequency modulated luminance signal is obtained by frequency-modulating a luminance signal which is separated from a composite color video signal of a standard system such as the NTSC, PAL, and SECAM systems. On the other hand, the frequency converted carrier chrominance signal is obtained by frequency-converting or counting down a carrier chrominance signal which is separated from the composite color video signal to a low-frequency range. In order to obtain a high recording density, no guard band is formed or a guard band of an extremely narrow width is formed between two adjacent video tracks.
It is possible to eliminate the need for a guard band or make the width of the guard band extremely narrow, because the frequency division multiplexed signal is hardly reproduced from the adjacent tracks due to the azimuth loss effect when the video tracks are successively and alternately scanned by the pair of rotary heads having the gaps of mutually different azimuth angles. However, although the azimuth loss effect is sufficient with respect to high-frequency components, the azimuth loss effect is insufficient with respect to low-frequency components. As a result, there is a problem in that the frequency converted carrier chrominance signal within the frequency division multiplexed signal, which is in the low-frequency range, is reproduced from the adjacent tracks as crosstalk.
In order to eliminate the problem described above, a recording and/or reproducing system was previously proposed in a U.S. Pat. No. 4,178,606 in which the assignee is the same as the assignee of the present application. According to this previously propossed system, the phase of the chrominance subcarrier of the frequency converted carrier chrominance signal which is obtained by frequency-converting the carrier chrominance signal of the NTSC or PAL system, is shifted by approximately 90.degree. in a predetermined direction for every one horizontal scanning period (1H) when carrying out the recording with respect to one of the two adjacent tracks, and is shifted by approximately 90.degree. in a direction opposite to the predetermined direction for every 1H when carrying out the recording with respect to the other of the two adjacent tracks in the case of the NTSC system carrier chrominance signal and is not shifted when carrying out the recording with respect to the other of the two adjacent tracks in the case of the PAL system carrier chrominance signal. A phase shift process complementary to the phase shift process performed at the time of the recording, is performed at the time of the reproduction. The frequency converted carrier chrominance signal which is reproduced as crosstalk from the adjacent tracks, is eliminated by the phase shift process and by the use of a comb filter.
In the previously proposed system, an analog circuit is used to perform the phase shift process. A pulse signal in which the phase is shifted by 90.degree. for every 1H and which has a repetition frequency of 40f.sub.H, for example, where f.sub.H represents the horizontal scanning frequency, and an output signal of an oscillator having the same frequency as the chrominance subcarrier, are respectively subjected to a frequency conversion in a first frequency converter. An output signal of the first frequency converter is supplied to an analog bandpass filter which produces a frequency component corresponding to a sum of the frequencies of the two signals supplied to the first frequency converter. The output frequency component of the analog bandpass filter and the carrier chrominance signal are subjected to a frequency conversion in a second frequency converter, and a frequency component corresponding to a frequency difference between the two signals, that is, the frequency converted carrier chrominance signal, is obtained from the second frequency converter.
However, the passband of the bandpass filter is selected to a relatively narrow band, so as to eliminate unwanted components and noise. Hence, even when the phase of the output signal of the first frequency converter supplied to the bandpass filter is accurately shifted by 90.degree. for every 1H, the waveform of the output frequency component of the bandpass filter becomes rounded at switching points where the phase switches. This rounded waveform of the output frequency component of the bandpass filter sometimes affects the phase of the color burst signal within the frequency converted carrier chrominance signal.